This invention relates generally to injection molding and more particularly to a nozzle for multi-cavity molding having superior heating adjacent the melt channel outlets.
Multi-cavity injection molding is often provided by having a melt passage or channel branch in a heated manifold to several different nozzles. One example of this is shown in the applicants' U.S. Pat. No. 4,424,622 which issued Jan. 10, 1984. It is also known to provide for multi-cavity edge gating by having the melt passage or channel branch in the nozzle itself. This is shown in Gellert U.S. Pat. No. 4,344,750 which issued Aug. 17, 1982. While these nozzles have an integral electrical heating element, they have the disadvantage that adequate balanced heat is not provided around the different branches and outlets of the melt passage. This has become a more serious problem with the increasing demand to mold more temperature critical materials. An attempt to overcome this problem is shown in Gellert U.S. Pat. No. 4,921,708 which issued May 1, 1990. It shows the nozzle having a number of spaced conductive probes, one aligned with each gate. After the melt flows centrally through the nozzle, it branches outward around each of the conductive probes and through the respective gate. However, this nozzle does not provide sufficient heat for all applications. Also, the large areas of liquid melt apply so much back pressure against the manifold that leakage can result at high pressure.